Flexure mounting for friction wheel measuring devices

ABSTRACT

A mounting and biasing mechanism for maintaining an essentially constant tracking force between a frictionally driven wheel and a measurement surface, along which the wheel rolls, is described. The mechanism includes a base member and a carrier member having resilient means operatively coupled between them for biasing the carrier member relative to the base member along a predetermined path of movement defined for the carrier member. The predetermined path of movement of the carrier member is defined by flexure means connected between the base and carrier members. The flexure means is arranged to define three spaced laterally deflectable columns, aligned normal to the path of movement between the base and carrier members, to provide three essentially frictionless, highly compliant points of connection between the base and carrier members.

United States Patent [1 1 Culver [4 1 June 26, 1973 [54] FLEXUREMOUNTING FOR FRICTION 1,038,770 9/1912 Locke 33/147 C WHEEL MEASURINGDEVICES Primary Examiner-Harry N. Haroian [75] Inventor. 2:5? H. Culver,Playa Del Rey, Attorney Hayden A. Carney [7 3] Assignees: Primus Mfg.,Inc., San Lorenzo, [57 ABSTRACT i' 'k g g lndusmes A mounting andbiasing mechanism for maintaining an OS nge a l essentially constanttracking force between a friction- {22] Filed: July 2, 1971 ally drivenwheel and a measurement surfaceQalong which the wheel rolls, isdescribed. The mechanism in- [211 Appl' 159201 cludes a base member anda carrier member having re- Related U.S. Application Data silient meansoperatively coupled between them for bi- 5 gominuationdmpm of Sen 67379Aug 27 asing the carrier member relative to the base member 1970, whichis a continuation-in-part of Ser. No. along a predetermined P Ofmovement defined for 9,872, Feb. 8, 1970. the carrier member. Thepredetermined path of movement of the carrier member is defined byflexure means [52] U5. Cl 33/141 R c nne ted etween he b se and carriermembers. The [51] Int-Cl. G01b 3/12 flexure means is arranged to definethree spaced later- [58] Field of Search 33/125, 141; ally deflectablecolumns, aligned normal to the path of I 267/160 movement between thebase and carrier members, to provide three essentially frictionless,highly compliant [56] References Cited points of connection betweenthebase and carrier UNITED STATES PATENTS members- 3,311,985 4/1967Hodge 33/141 A 10 Claims, 7 Drawing Figures FLEXURE MOUNTING FORFRICTION WHEEL MEASURING DEVICES CROSS-REFERENCE TO RELATED APPLICATIONSThis application is a continuation-in-part of copending application Ser.No. 67,379 filed Aug. 27, 1970 as a continuation-in-part of applicationSer. No. 9,872 filed Feb. 8, 1970.

It is believed that full understanding of this invention will befacilitated by reference to U.S. Pat. Nos. 3,307,265, 3,378,929,3,561,120 and 3,561,121. U.S. Pat. Nos. 3,307,265 and 3,378,929 and3,561,121, in combination with each other, describe the presentlypreferred form of the commonest type of measuring device with which thisinvention has utility. U.S. Pat. No. 3,561,120 describes a presentlypreferred alignment method with which a mounting assembly according tothis invention may be used.

BACKGROUND OF THE INVENTION This invention pertains to precisiondistance and related measurements through the use of friction wheelmeasuring devices. More specifically, this invention pertains to animproved assembly for mounting the measuring device for tracking of thefrictionally driven wheel thereof along a measurement surface withessentially constant tracking force.

DESCRIPTION OF THE PRIOR ART A widely used friction wheel measuringdevice is described in U.S. Pat. No. 3,378,929. A common use of frictionwheel measuring devices is in combination with machine tools where thedevices are used to measure the distance one part of a machine tool ismoved relative to another part of the tool. For example, a frictionwheel measuring device is often mounted to a lathe carriage to engage aguideway surface of the lathe bed to measure the distance the carriageis moved along the lathe bed. Such devices, however, are not restrictedto use on lathes and have in fact found many other uses including usesin other types of machine tools, in coordinate measuring machines, indiameter measuring systems, and in systems for measuring-angles aroundthe center of a rotary table or other cylindrical member.

In order that frictionwheel measuring devices of the type described inU.S. Pat. No. 3,378,929 may be used to produce measurements in whichconfidence may be placed, it is necessary that the device operate toproduce both accurate measurements and repeatable measurements.Measurement accuracy is achieved principally by the precision with whichthe components of the measuring device are fabricated. Measurementaccuracy is also achieved by use of the structures and techniquesdescribed in U.S. Pat. Nos. 3,307,365 and 3,561,121, for example.Measurement accuracy is achieved when the measurement produced by thedevice as the friction wheel tracks a given distance over themeasurement surface is exactly the same as the extent of the givendistance. v

A repeatability error; on the other hand, is a failure of the measuringdevice to read zero" when returned to a zero postiion" after severalcycles of motion away from and back to the zero position on themeasurement surface, preferably under conditions where each cycleinvolves plural rotations of the friction wheel. It has been ascertainedthat repeatability errors are produced primarily by the environment ofthe measuring device rather than by any deficiencies in the deviceitself. Lack of repeatability can be quite troublesome when themeasuring device is used in the machining of a complex part on a largemachine tool, which machining process may require several days work by askilled machinist.

It has been found that repeatability errors are generated primarily bynon-reciprocal deflections produced in the components of the machinetool with which the measuring device is used, which components wereformerly thought to be absolutely rigid, and also by similarnon-reciprocal deflections in the supporting bracketry and mountingassemblies provided for the measuring device; the latter deflections areproduced as second order effects of the non-reciprocal deflectionsencountered in the structure of the machine tool. Such deflectionsadmittedly are very slight, but they are sufficient in magnitude toproduce repeatability errors in a friction wheel measuring deviceoperated cyclically over long distances of travel.

The nature of the non-reciprocal deflections productive of repeatabilityerrors is described more fully in U.S. Pat. No. 3,561,120. Brieflysummarized, however, repeatability errors are produced by one or more ofthree causative factors: (1) tracking of the friction wheel skew to thedirection of gross relative movement between a lathe bed and a lathecarriage, for example; (2) variations in the pitch of the metering wheelrelative to the measurement surface; and (3) variations in the force ofengagement of the metering wheel with the measurement surface.Variations in the pitch of the metering wheel are significant because itis preferred that the peripheral surface of the wheel be defined as aportion of a sphere rather than as a portion of right circular cylinderfor the reasons described in U.S. Pat. Nos. 3,307,265 and 3,561,121.

The mounting mechanisms initially used with friction wheel distancemeasuring devices are typified by the mounting mechanism described inU.S. Pat. No. 3,378,929. These initial mounting mechanisms werecharacterized by the use of stiff springs which were biased to providethe desired wheel tracking and engagement force. In any spring, theforce. developed by the spring is equal to the effective stiffness ofthe spring times the amount of deflection of the spring. If the springhas high stiffness, a small deflection of the spring corresponds to alarge force being developed by the spring or applied to the spring.

It has long been recognized that repeatable and accu rate measurementsare produced by friction wheel measuring devices when the measuringdevice is free from changes in the attitude of the friction wheelrelative to the measurement surface during the measurement process.Changes in this attitude result when the measuring device moves inresponse to deflections in the machine tool and in the mounting assemblyused to connect the measuring device to the machine tool. Thesedeflections are in turn produced by variations in the forces applied tothe machine tool and to the mounting mechanisms.

Once the above-listed causative factors of repeatability errors wereidentified, the mounting mechanism described in copending applicationSer. No. 67,379 was developed. This improved mounting mechanism providesthe desired tracking force between the friction wheel and themeasurement surface by the use of a spring which develops essentiallyconstant force when subjected to substantial deflection; specifically,the biasing spring of this improved mounting mechanism is provided inthe form of a resilient column preloaded to a load exceeding thecritical load of the column. The result is that the effective biasingforce manifested between the friction wheel and the measurement surfaceis essentially constant throughout substantial relative movement of theparts of the mounting mechanism between which the column spring isengaged.

The basic objective sought to be achieved in the structure of theimproved mounting mechanism described in copending application Ser. No.67,379 is to provide a mounting mechanism which is stiff in five of thesix modes of orthogonal motion, but which is soft in the sixth mode ofsuch motion. The six modes of orthogonal movement are movements linearlyalong each of three orthogonal axes and movements angularly about eachof the three orthogonal axes, i.e., the conventional mutuallyperpendicular X, Y and Z axes. Specifically, the mounting mechanismdescribed in application Ser. No. 67,379 is arranged in use so that thepermitted single degree of motion is linearly along a line normal to themeasurement surface.

It has been found that the mounting mechanism described in applicationSer. No. 67,379 has a susceptibility to softness,'i.e., to internaldeflection, in response to moments applied to it about the axis alongwhich linear motion is permitted. Such'deflections of the mountingmechanism result in the generation of the first causative factor listedabove concerning repeatability errors.

SUMMARY OF THE INVENTION This invention provides an improved mountingmechanism of the basic type described in copending application Ser. No.67,379 and is addressed to the same basic objective so that identifiedabove, namely, the production of a mounting mechanism which is stiff infive of the six modes of orthogonal motion but which is soft andcompliant to deflections and movements in the sixth mode. The presentmounting mechanism achieves this objective to a considerably greaterextent than was achieved by the mounting mechanism described inapplication Ser. No. 67,379. Thus, the present mounting mechanismprovides all of the benefits and advantages heretofore provided by themounting mechanism described in Ser. No. 67,379 without theabove-described disadvantage recently discerned in this prior mountingmechanism. The present mounting mechanism is stiff to deflectionscorresponding to the one mode of undesired movement which is mosttroublesome to measurement accuracy and repeatability.

Generally speaking, this invention provides a mounting assembly for afriction wheel measuring device and includes a base member adapted to bemounted to one of two relatively movable elements to the other of whichthe measuring device is to be engaged. The mounting assembly alsoincludes a carrier member disposed adjacent the base member and definingmeans for releasably clamping a measuring device thereto. Resilientmeans are operatively coupled between the base member and the carriermember for biasing the carrier member relative to the base member alonga predetermined path of movement defined for the carrier member. Themounting assembly further includes flexure means which are connectedbetween the base frictionless points of connection between the base andcarrier members.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other featuresof the in' vention are more fully set forth in the following detailedexplanation and description of a presently preferred embodiment of theinvention, which explanation and description is presented with referenceto the accompanying drawings wherein:

FIG. 1 is an elevation view, partially in section, show ing a mountingmechanism according to the description of application Ser. No. 67,379;FIG. 1 is presented in furtherance of an explanation of the problemovercome by this invention;

FIG. 2 is an elevation view taken along line 2-2 in FIG. 1;

FIG. 3 is a view similar to that of FIG. 2 illustrating the source ofthe problem overcome by this invention;

FIG. 4 is a perspective view of one of the identical flexure platesencountered in the mounting mechanism of FIG. 1 as deflected in responseto the condition illustrated in FIG. 3;

FIG. 5 is an elevation view of one of the presently preferred improvedflexure plates of a mounting assembly according to this invention;

FIG. 6 is an elevation view of the other of the presently preferredflexure plates of a mounting assembly according to this invention; and

FIG. 7 is an enlarged cross-sectional elevation view illustrating theconnection of the present flexure plates to the structure of themounting assembly.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT FIG. 1 illustrates themounting of a friction wheel measuring device 10 to a lathe carriage 11,for example, by a mounting assembly 12 according to the disclosure ofapplication Ser. No. 67,379 so that the measuring device functions tomeasure the distancewhich the lathe carriage moves relative to a lathebed 13. The direction in which the carriage moves along the lathe bed isreferred to herein as the direction of gross relative movement of themeasuring device. The measuring device includes a housing 14 withinwhich is rotatably mounted a circular metering wheel 15 of controlledcircumferential characteristic. The periphery of the metering wheelpreferably has a curved profile, as shown, for the reasons set forth inUS. Pat. No. 3,561,121. The metering wheel is mounted in the housing sothat, during use of measuring device 10, the rim of the wheel projectsthrough a front face 16 of the housing and frictionally contacts ameasurement surface 17,defined by the lathe bed and along whichmeasurements are to be made of the amount of travel of the lathecarriage relative to the bed.

A gross measurement indicator dial 18, calibrated in any desiredmeasurement scale such as inches, is disposed on the upper surface ofhousing 14 and is coupled directly to theshaft (not shown, but see US.Pat. No. 3,378,929) which supports the metering wheel. A

fine measurement indicator 19 for indicating small increments ofmeasured travel is also mounted to the upper surface of the housing.Indicator 19 includes a dial plate (not shown), calibrated, for example,in hundredths and thousandths of an inch, and a rotatable pointer (notshown) which cooperates with the dial plate and which is coupled to themetering wheel via an anti-backlashed motion amplifying gear train (notshown), for example; see U.S. Pat. No. 3,378,929. Any angular movementof the metering wheel is immediately manifested by indicators 18 and 19which, in combination, serve to indicate the distance which the meteringwheel has travelled along the measurement surface. I

A photo-electric signal generator 20 is located between indicator 19 andhousing 14 coaxially of the output shaft of the gear train. Signalgenerator 20 operates in response to rotation of wheel 15 to generate aseries of signals which correspond to discrete increments of thedistance which wheel 15 rolls along measurement surface 17 during themeasurement process. The signals developed in signal generator 20 aresupplied via a suitable cable 21 to a remote display panel (not shown).It is 'within the scope of this invention that measuring device may beprovided in a form which does not include signal generator 20 or in aform which does not include visual'indicators l8 and 19; in the formercase the measuring device has no remote readout capacity, whereas in thelatter case the device has no capacity to present a measurement readoutat the location of housing 14.

A male dovetail member 24 is secured to the underside of housing 14 andhas its length aligned parallel to the elongate extent of housing 14,which extent is also preferably disposed perpendicular to measurementsurface 17 during use of the measuring device. The male dovetail memberis slidably positioned in a female dovetail groove 25, see FIG. 3,provided in the upper surface of a carrier member 26 of mountingassembly 12. Carrier member 26 forms the upper one of two majorcomponents of mounting assembly 12. The other major component of themounting assembly is defined by a base member 27 which has its lowersurface mounted to a plate 28 by bolts 29.

The lower end of a mounting pedestal 30 is securely fastened to lathecarriage 11 by bolts 31. The upper end of the pedestal defines aperipheral flange 32. A pair of set-screws 33 are threaded throughflange 32 along a line perpendicular to measurement surface 17 to abut,but not penetrate, the lower surface of plate 28. Flange 32 is coupledto plate 28 by a pair of bolts 34, only one of which is shown, locatedalong a line parallel to the measurement surface. Screws 33 areadjustable in flange 32 to vary the pitch of the plane of rotation ofwheel relative to measurement surface so that the effectivecircumference of wheel 15 relative to its maximum circumference may. beselected for the reasons set forth in US. Pat. Nos. 3,307,265 and3,561,121. Bolts 34 are adjustable in flange 32 to vary the tilt ofmeasuring device 14 about its longitudinal axis, thereby to define theprecise corrective angle of skew tracking of the metering wheel relativeto the direction of gross relative movement of the measuring devicealong measurement surface 17 during the measurement process; the natureof and reason for this adjustment is described in U.S. Pat. No.3,561,120.

A pair of thin spring-metal flexure plates 36 interconnect the adjacentends of carrier member 27 and base member 27 to couple the members toeach other for movement of the members relative to each other only alonga line normal to the measurement surface, i.e., along a line parallel tothe length of male dovetail member 24. The flexure plates are sointerconnected between the carrier and base members of mounting assembly12 that the members are spaced from each other. by the flexure plates.The lower surface of carrier member 26 and the upper surface of basemember 27 are configured to define a cavity 37 between them when themembers are secured to each other, as shown, by flexure plates 36.

Disposed within cavity 37 is an elongate sheet 38 of spring metal whichhas its opposite ends in abutting, but not fixed, contact with the lowerportions of carrier member 26 adjacent measurement surface 17 and withthe upper extent of mounting member 27 remote from the measurementsurface, i.e., adjacent the rear of the mounting assembly. In otherwords, the resilient sheet 38 is loaded as a column and is thereforereferred to herein as a column spring or an Euler spring. The columnspring is arranged within cavity 37 so that a line between its ends ismore nearly parallel to the length of male dovetail 24 thanperpendicular to the male dovetail. Windows 39 are provided through thecarrier and base members of the mounting assembly on either side of thecolumn spring to allow a machinist or other user of the mountingassembly to view deflections in the column spring.

The rear end of male dovetail member 24 is engageable in abuttingrelation with a screw 40 which is mounted in a substantially rigidnon-resilient U-shaped yoke 41, the ends of which are pivoted at 42 tothe rear end of carrier member 26 on opposite sides of female dovetailgroove 25. Screw 40 is rotatable by manual operation of a knob 43carried by the screw rearwardly of yoke 41.

As shown in FIG. 2, each of flexure plates 36 is provided as arectangular piece of thin spring metal. As shown in FIG. 1, flexureplates 36 are disposed parallel to each other. When mounting assembly 12is properly installed on lathe carriage l1, flexure plates 36 lieessentially parallel to measurement surface 17 adjacent the point atwhich the periphery of friction wheel 15 engages the measurementsurface. It is apparent therefore that flexure plates 36 prevent carriermember 26 from moving linearly toward or away from base member 27, i.e.,the flexure plates prevent the base and carrier members from movinglinearly along the line defined as the Y axis; see FIG. 1. Also, theflexure platesprevent carrier member 26 from moving laterally relativeto base member 27 along a line defined parallel to the X axis whichcorresponds to the direction of the gross relative movement of measuringdevice 10 along measurement surface 17; that is, the flexure platesprevent the carrier member from moving in a direction parallel to theplanes of flexure plates 36 and parallel to the plane of rotation ofmetering wheel 15. Further, the flexure plates prevent the base andcarrier members from moving angularly relative to each other about linesparallel to either of the X or Y axes; they also function to inhibitangular movement of the carrier member about lines parallel to the Zaxis. On the other hand, because the flexure plates are fabricated ofthin resilient metal and are secured to the carrier and base membersalong only their upper and lower edges, respectively, it is apparentthat the flexure plates permit the carrier member to move laterallyrelative to the base member along a line parallel to the Z axis; the Zaxis is defined normal to the measurement surface at the point ofcontact of the friction wheel with the measurement surface. Thus, fromthe foregoing it is apparent that the flexure plates, by reason of theirgeometry and disposition in mounting assembly 12, should constrain thecarrier member from movement relative to the base member in five of thesix modes of orthogonal motion possible, but permit and are soft tomovement of the carrier member relative to the base member in the sixthmode of orthogonal movement, i.e., linear movement parallel to the Zaxis. (In reality, as shown below, flexure plates 36 exhibit anundesired softness to angular movement of the carrier member about aline parallel to the Z axis, and this undesired softness is eliminatedby the improved mounting assembly described below.)

Column spring 38 is defined so that its critical load (see for example,Elements of Strength of Materials by Timoshenko and MacCullough, onevolume, D. Van Nostrand Company, Inc., New York, third edition, 1949,pp. 288-291) has a magnitude which is only slightly less than thedesired force of tracking engagement of friction wheel 15 againstmeasurement surface 17.

In use of mounting assembly 12, measuring device is engaged to themounting assembly by engaging male dovetail 24 in female dovetail groove25, by sliding the measuring device toward the measurement surface untilthe friction wheel engages the measurement surface, by engaging theforward end of screw 40 with the rear end of male dovetail 34, and thenby tightening down knob 43 to, in effect, pull carrier member 26rearwardly along male dovetail 24. Such operation of knob 43 causes acompressive load to be applied to column spring 38. When thiscompressive load reaches the critical load of the column spring,thecolumn spring buckles; thereafter, operation of knob 43 causescarrier member 36 to be moved rearwardly parallel to the Z axis relativeto base member 27 while'the reactive force applied by the buckled columnspring to the carrier member remains essentially constant. That is, oncethe column spring has been buckled, it appliessubstantially constantforce between the carrier and base members throughout substantialincrements of movement of these members relative to each other. It isapparent, therefore, that the force applied by the column spring, viacarrier member 26 and housing 14, to urge friction wheel 15 intocontactwith measurement surface 17 is an essentially constant forcethroughout substantial increments of movement of measurement device 10along the Z axis relative to the measurement surface.

In use, knob'43 is operated about one or two turns after column spring38 first buckles so that a predetermined amount of buckle is imposedinto the column spring before male dovetail member 24 is locked intoposition in female dovetail groove 25 in the manner described below.Thereafter, no relative movement between housing 14 and carrier member26 is possible; measuring device 10 may then be operated to perform thedesired measurements after the alignment process described in Patent No.3,561,120 has been completed.

FIG. 2 shows that the configuration of female dovetail groove 25, in theupper extent of carrier member 26, includes a pair of upwardly open landsurfaces along opposite sides of the groove for registry with the lowersurfaces of male dovetail 24. The side walls 46 of groove 25 slopeupwardly toward each other and are defined by the opposing surfaces of apair of laterally deflectable locking gibs 47 formed in the upper extentof carrier member 26. Thus, each gib 47 is defined between a groove 48which extends into the carrier member between dovetail groove side wall46 and land surface 45. The opposite lateral boundary of each gib 47 isdefined by a groove 49 formed in the upper surface of the carrier memberparallel to but inwardly from the sides of the carrier member. Theresultis that the base of each gib 47 is of reduced width which isselected so that the gib is laterally deflectable like a cantileveredbeam about its base between the bottoms of grooves 48 and 49. A rib 50is defined between each groove 49 and the adjacent side of the carriermember. A setscrew 51 is threaded through each rib 50 adjacent each endthereofinto abutting engagement with the adjacent surface of gib 47. Itis apparent, therefore, that as screws 51 are turned to advance intoribs 50, the ends of the screws apply a lateral force to locking gibs 47causing the gibs to deflect toward dovetail groove 25. Setscrews 51therefore are operable to cause the male dovetail 24 to be securely yetreleasably clamped in female dovetail groove 25 after the desired degreeof buckle has been imposed upon column spring 38 in the manner describedabove.

Mounting assembly 12, shown in FIGS. 1 and 2 and described above, is inaccord with the disclosures of copending application Ser. No. 67,379.The structure described above does not reflect the improvement made bythis invention. The improvement provided by this invention resides in amodification of flexure plates 36 of mounting assembly 12. The structureshown in FIGS. 1 and 2 has been described above in detail so that thenature of the problem overcome by this invention may be understood, andso that the significance of the improvement provided by this inventionmay be fully appreciated.

The problem solved by this invention arises as locking gibs 47 aretightened against the side walls of male dovetail 24 in response to theturning of setscrews 51. It is desired that male dovetail 24 be securelyand rigidly clamped within female dovetail groove 25. To accomplishthis, substantial force must be applied by gibs V 47 to the side wallsof male dovetail 24, and this force necessarily must have a reactionforce in the structure of carrier member 26. This situation isillustrated in FIG. 3 which shows, in grossly exaggerated form for thepurposes of illustration, that as screws 51 are tightened against theouter surfaces of gibs 47, grooves 48 and 49 tend to open as gibs 47tend to react away from dovetail 24 and as ribs 50 tend to react awayfrom gibs 47 in response to the force applied by screws 51 to the outersurfaces of the gibs. The necessary effect of these deflections,occurring in the upper portions of the structure of carrier member 26,is to induce the carrier member to buckle so that the normallyhorizontal upper edge of flexure member 36 is induced to assume acurvature (represented by arc S5 in FIG. 3) concave to the upper surfaceof base member 27. In other words, the reaction forces developed incarrier member 26 by reason of securely clamping measuring device 10 tothe carrier member causes the carrier member to tend to'buckle in suchmanner that the outer edges of the carrier member move downwardlyrelative to the center of the carrier member. Such buckling of thecarrier member can occur only if flexure plates 36 deflect toaccommodate this displacement of the outer edges of the carrier relativeto the center portions of the carrier member; such deflection of flexureplates 36 of a mounting assembly according to disclosures of copendingapplication Ser. No. 67,379 is illustrated in FIG.'4.

As shown in FIG. 4, each of flexure plates 36 of mounting assembly 12have upper, lower and opposite side edges 56, 57, 58 and 59,respectively. As carrier member 26 tends to buckle or deflect in themanner illustrated in FIG. 3, the center of flexure plate top edge 56tends to move upwardly relative to its ends. Because the lower edge offlexure plate 36is securely connected along its length to base member27, as shown in FIG.

' 2, flexure plate'edge 57 tends to remain straight. The

result is that flexure plate 36 is induced to buckle along its sideedges 58 and 59,'but to remain straight andunbuckled intermediate-sideedges 58' and 59; this condition is shown in FIG. 4. The character ofthe deflection of carrier plate 26, as shown in FIG. 3, acts in themanner shown in FIG. 4 upon both thefront and rear flexaxis is reduced;if the flexure plates are in fact buckled in the manner illustrated inFIG. 4, then the resistance of the flexure plates to moments about the Zaxis is nearly'elimina'te'd; The ultimate result of these phenomcm. isthat mounting assembly 12 is not as resistant as desired to momentsapplied thereto about-the Z axis and, in use,the mounting assemblyresponds'ortends to respond to suchfmoments to produce variations in thedesired corrective angle of skew tracking of the friction wheel 15 alongmeasurement surface 17.

Moments about the Z axis are applied to mounting assembly l2duringoperation because of the drag of friction wheel 15 along measurementsurface 17; preferably, the force of engagement of friction wheel 15with measurement surface 17 is on the order of 40 lbs. and this force isconcentrated in a very small area of actual physical contact betweenthewheel and the measurement surface. '(Also, moments about the Z axistend to be generated by reason of the'curved profile of the frictionwheel and by reason of the presence of the corrective-skew tracking.angle relative to the direction of gross relative movement of themeasuring device along measurement surface 17.) Due to the'geometry byreason of thefdeflections illustrated in FIGS. 3 and The susceptibilityof mounting assembly 12 to moments about the Z axismay be described-bestby visualizing the effect in three separate areas 61, 62 and 63 of aflexure plate 36 buckled in response to the condition illustratedby,FlG. 3. Consider central columnar strip 61 of flexure plate 36 andend columnar strips 62 and 63 of the flexure plate, and imagine that.the portions of the flexure plate between these columnar strips areeliminated so that carrier member 26 is connected at each of its ends tobase member 27 by three laterally resilient, thin columns. As carriermember 26 deflects in the manner shown in FIG. 3, strip 61 is placedunder tension as the central portion of the carrier member movesupwardly relative to the side portions thereof to which strips 62 and 63are connected. The result is that strips 62 and 63 are placed undercompressive loadings which may readily exceed the critical (Euler) loadsof the strips considered as columns, with the result that strips 62buckle, as shown in FIG. 4. The compressive 26 could move freelyupwardly relative to strips 62 and I 63, by hypothesis, however, thiscannot be the case because the central portions of carrier member 26 andbase member'27 are interconnected at their opposite ends by columnarstrips 61. The result is that when carrier member 26 of mountingassembly 12 includes the simple rectangular flexure plates 36 and thecarrier plate is deflected as shown in FIG. 3, central strips 61 of theflexureplates behave as fulcrums for angular inotion of the carriermember relative to base member 27, and such angular motion is resistedby strips 62 and 63 behaving in much the same manner as column spring Itshould be emphasized at this point that FIGS. 3 and 4 constitute grossexaggerations of the effects encountered during the use of mountingassembly 12 and that the end strips of flexure plate 36 may not actuallybuckle as shown in- FIG. 4. The end strips of plates 36, however, aresubjected to compressive loadings which reduces their ability to resistmoments applied to the mounting assembly about the Z axis, therebyrendering the mounting assembly less resistant than desired to suchmoments. This means that flexure plates 36 tend to permit actualvariations, from moment, to moment, in the corrective skew trackingangle of friction wheel 15 as it rolls during an actualmeasurement alongmeasurementsurface 17, thereby producing errors, albeit slight, inmeasurement accuracy'and measurement repeatability. These errors areeliminated by modifying the structure of the flexure plates for,mounting assembly 12 in the manner shownin FIGS. 5' and 6. a

Flexure plate 65, shown in FIG. 5 (as well as flexure plate 66, shown inFIG. 6), preferably is defined of thin resilientmetal stock which isabout 66 to 100 percent thicker than the stock material of which flexureplates 36 are fabricated. Thus, flexure plates 66 and have approximatelythe same resistance to linear movements of carrier'member 26 linearlyparallel to the Z axis relative to base member 27 as-flexure plates36. i

As shown in FIG. 5, flexure plate 65 has an overall width and heightequal to the corresponding dimension of flexure plate 36 and has upperand lower edges 67 and .68, respectively. Flexure plate 65 iscontiguredto define strip sections 69 which extend along the upper andloweredges of the plate. Flexure plate 65 is also configured to define apair of diverging leg sections 70 which have a common point ofconnection at 71 to upper strip section 69 at the-midpoint of section69.

lower ends of leg sections 70 are connected to the lower strip sectionapproximately midway between the,

Y midpoint of thelower strip section and the opposite ends of theflexure plate. A pluralityof holes 64 are formed through strip sections69 at substantially regu- [at intervals along their length. 'It ispreferred that flexure plate 65 be used in lieu of plate 36 at theforward end of mounting assembly 12, i.e., at the end of the mountingassembly which normally is disposed adjacent measurement surface 17.

Flexure plate 66, as shown in FIG. 6, has upper and lower marginal stripsections 69fassociated with the upper and lower edges71 and 72 of thisimproved flexure plate. In flexure plate 66, strip sections 69 arebounded adjacent the center of the flexure plate by parallel slots 73formed through the flexure plate. Each of slots 73 has opposite ends 74which are located inwardly of the adjacent side edges 75 of the plate.Ac-

7 cordingly, flexure plate 66 is configured to define a pair of columnportions 76 at each end thereof and a brace portion 77 which extendsbetween slots 73 and interconnects the column portions along theircentral parts.

tions 69 of flexure plate 66 at regular intervals along :the length ofthe strip portions. Flexure plate 66 preferably is installed in mountingassembly 12 in place of the flexure plate 36 atthe rear end of themounting assembly, i.e., at the end of the assembly which normally islocated remote from measurement surface 17.

- Asshown in .FIG. 7, flexure plate 66 is interconnected between carriermember 26 and base member 27 by theuse of screws 80 inserted throughholes 64 of the plate and threaded into-tapped holes provided in thecarrier and base members. Preferably a back-up strip 81 is interposedbetween the heads of screws 80 .and the strip sections of the flexureplate to distribute 'the clamping action of the screws along the lengthof the strip sections. Flexure plate 65 is similarly mounted between thefront ends of the carrier and base members.-

It will be apparentfrom the foregoing description that when mountingassembly 12 is modified by the substitution of flexure plates 65 and 66thereinto in place of simple rectangular flexure plates 36,v themountingassembly provides three spaced, essentially frictionless points ofconnection between-the base and carrier members. These points of.connection are essentially frictionless because thefonly movementencountered in these points is resilient bending of leg portions 70 orcolumn portions 76, respectively, as carrier member 26 translatesrelative to base member 27 parallel to the Z axis. Because a three-pointconnection between the base and carrier members is provided, neither theJinverted V column arrangement defined by flexure plate 65 northestraight column arrangements provided by portion 76 of flexure plate66 can be subjected to any compressive load by reason of the buckling ofcarrier member 26 in the manner shown in FIG. 3. The result is that amounting assembly incorporating flexure plates 65 and 66 isnotsusceptible to deflection in response to moments applied, to it aboutthe Z axis. Accordingly, a mounting assembly incorporating flexureplates 65 and 66 effectively meets the basic objective of providing anassembly which is stiff in five of the six modes of orthogonal motion,but which has a desired softness to the sixth mode of motion. The resultis that no variations in the corrective skew tracking angle programmedinto the installation by the practice of the method described in U.S.Pat. No. 3,561,120 are encountered as friction wheel 15 rolls alongmeasurement surface 17 during the measurement process.

Preferably, the three points of connection provided between carriermember 26 and base member 27 are distributed geometrically symmetricalabout the linear path of motion permitted between the carrier and basemembers and defined by flexure plates 65 and 66.

From the foregoing description, it is apparent that this inventionprovides a simple and effective solution to the problem encountered inthe structures described in application Ser. No. 67,379. This inventionproduces an economical solution to this problem because the practice ofthis invention requires only minor structural modifications to the basicstructure of the mounting'assembly described in this copendingapplication, rather than wholesale revision of such structure.

This invention may be used to advantage with any friction wheelmeasuring device in essentially any environment or installation. A lathehas been referred to above merely for the purposes of example.Similarly, it should be understood that the foregoing descriptionhas'been. presented with reference to a presently preferred measuringdevice manufactured by the assignee of this invention and availablecommercially under the trademark TRAV-A-DIAL. Workers skilled in the artto which this invention pertains will readily appreciate that thisinvention may be used to advantage in conjunction with measuring devicesother than TRAV-A- DIAL measuring devices and in conjunction withmounting assemblies for such other measuring devices. Accordingly, theforegoing description should not be considered as limiting the scope ofthis invention to the specific structures illustrated and described, butrather as illustrative of the principles of the invention.

What is claimed is:

l. A mounting assembly for a friction wheel measuring device comprisingl.'a base member adapted to be mounted to one of two relatively movableelements to the other of which the measuring device is to be engaged,

2. a carrier member disposed adjacent the base member and defining meansfor releasably clamping a measuring device thereto, I v I 3. resilientmeans operatively coupled between the base member and the carrier memberfor biasing the carrier member relative to the base member along apredetermined path of movement defined for the carrier member, and

4. flexure means connected between the base and carrier members fordefining said path, for restricting relative movement between the baseand carrier members to movement only along said path during normalconditions of use of the mounting assembly, and for effectively definingonly three spaced, essentially frictionless points of connection betweenthe base and carrier members.

'2. A mounting assembly according to claim 1 about the path.

members.

3. A mounting assembly according to claim 2 wherein the points ofconnection are defined geometrically symmetrically about the path.

4. A mounting assembly according to claim 3 wherein the flexure meanscomprises a first thin resilient flexure element defining one of thepoints of connection along the path and connected between adjacent endsof the base and carrier members, and a second thin resilient flexureelement connected between the opposite adjacent ends of base and carriermembers and defining the other two points of connection on oppositesides of the path.

5. A mounting assembly according to claim 4 wherein the points ofconnection are defined as columns normal to the path and laterallyresilient in directions parallel to the path.

6. A mounting assembly according to claim 5 wherein the respectiveflexure elements are configured to define means for inhibitingdeflection of the columns in the planes of the flexure elements.

7. A mounting assembly according to claim 1 wherein the resilient meansis effective to bias the carrier member inone direction along the pathrelative to the base member with a force which is essentially constantthroughout substantial movements between the 8. A mounting assemblyaccording to claim 7 wherein the resilient means is defined to operateas an axially loaded column to produce said force.

9. A mounting assembly according to claim 1 wherein the carrier memberdefines a female dovetail channel aligned with said path for receivingtherein cooperatively configured male dovetail projection means carriedby the measuring device.

10. A mounting assembly fora friction wheel measuring device having ahousing, the assembly comprising 1. a base member adapted to be mountedto one of two relatively movable elements to the other of which themeasuring device is to be engaged,

2. a carrier member disposed adjacent the base member and defining meansfor releasably clamping a measuring device thereto,

3. resilient means operatively coupled between the base member and thecarrier member for biasing the carrier member relative to the basemember along a predetermined path of movement defined for the carriermember, and

v 4. flexure means connected between the base and carrier members fordefining said path, for restricting relative movement between the baseand carrier members to movement only along said path during normalconditions of use of the mounting assembly, and for effectively definingonly three spaced, essentially frictionless points of connection betweenthe base and carrier members.

1. A mounting assembly for a friction wheel measuring devicecomprising
 1. a base member adapted to be mounted to one of tworelatively movable elements to the other of which the measuring deviceis to be engaged,
 2. a carrier member disposed adjacent the base memberand defining means for releasably clamping a measuring device thereto,3. resilient means operatively coupled between the base member and thecarrier member for biasing the carrier member relative to the basemember along a predetermined path of movement defined for the carriermember, and
 4. flexure means connected between the base and carriermembers for defining said path, for restricting relative movementbetween the base and carrier members to movement only along said pathduring normal conditions of use of the mounting assembly, and foreffectively defining only three spaced, essentially frictionless pointsof connection between the base and carrier members.
 2. a carrier memberdisposed adjacent the base member and defining means for releasablyclamping a measuring device thereto,
 2. a carrier member disposedadjacent the base member and defining means for releasably clamping ameasuring device thereto,
 2. A mounting assembly according to claim 1wherein the path is defined to be linear and the points of connectionare disposed effectively symmetrically about the path.
 3. A mountingassembly according to claim 2 wherein the points of connection aredefined geometrically symmetrically about the path.
 3. resilient meansoperatively coupled between the base member and the carrier member forbiasing the carrier member relative to the base member along apredetermined path of movement defined for the carrier member, and 3.resilient means operatively coupled between the base member and thecarrier member for biasing the carrier member relative to the basemember along a predetermined path of movement defined for the carriermember, and
 4. flexure means connected between the base and carriermembers for defining said path, for restricting relative movementbetween the base and carrier members to movement only along said pathduring normal conditions of use of the mounting assembly, and foreffectively defining only three spaced, essentially frictionless pointsof connection between the base and carrier members.
 4. A mountingassembly according to claim 3 wherein the flexure means comprises afirst thin resilient flexure element defining one of the points ofconnection along the path and connected between adjacent ends of thebase and carrier members, and a second thin resilient flexure elementconnected between the opposite adjacent ends of base and carrier membersand defining the other two points of connection on opposite sides of thepath.
 4. flexure means connected between the base and carrier membersfor defining said path, for restricting relative movement between thebase and carrier members to movement only along said path during normalconditions of use of the mounting assembly, and for effectively definingonly three spaced, essentially frictionless points of connection betweenthe base and carrier members.
 5. A mounting assembly according to claim4 wherein the points of connection are defined as columns normal to thepath and laterally resilient in directions parallel to the path.
 6. Amounting assembly according to claim 5 wherein the respective flexureelements are configured to define means for inhibiting deflection of thecolumns in the planes of the flexure elements.
 7. A mounting assemblyaccording to claim 1 wherein the resilient means is effective to biasthe carrier member in one direction along the path relative to the basemember with a force which is essentially constant througHout substantialmovements between the members.
 8. A mounting assembly according to claim7 wherein the resilient means is defined to operate as an axially loadedcolumn to produce said force.
 9. A mounting assembly according to claim1 wherein the carrier member defines a female dovetail channel alignedwith said path for receiving therein cooperatively configured maledovetail projection means carried by the measuring device.
 10. Amounting assembly for a friction wheel measuring device having ahousing, the assembly comprising